The present invention relates to a semiconductor device and a testing method thereof and, especially, to a technique effectively applied to both of a semiconductor device such as a LCD driver having a function of driving gate lines of a liquid crystal display panel and a testing method thereof.
Techniques that the inventors of the present invention have examined on the premise of the present invention will be described using FIGS. 16 to 19. FIG. 16 is a view showing a connection relation between a liquid crystal display panel and a LCD driver; FIG. 17 is a view showing a connection relation between a LCD driver and a semiconductor test equipment; FIG. 18 is a view showing a configuration of the inverter circuit 30 in FIG. 17; and FIG. 19 is a view showing an operation of a gate output of a LCD driver.
As shown in FIG. 16, a liquid crystal display panel 500 and a LCD driver for driving the liquid crystal display panel 500 are connected. A transistor 511 and a capacitor 512 are disposed in each pixel 510 of the liquid crystal display panel 500 in the form of this Figure. A source terminal of each of the transistors arranged vertically in Figure is used in common. Similarly, a gate terminal of each of the transistors arranged horizontally in Figure is also used in common.
Generally, in order to drive the liquid crystal display panel 500, there are required: a source driver 501 connected to a source common terminal and having a function of applying a gray-scale voltage acting as color display information; a gate driver 502 connected a gate common terminal and having a function of executing display control of horizontal pixels shown in Figure; and a power supply circuit 503 having a function of generating a voltage required to drive the source driver 501 and the gate driver 502. These are generally called a LCD driver, wherein the source driver 501, the gate driver 502, and the power supply circuit 503 may be individually integrated or may be integrated on one chip by consolidating the several functions.
As shown in FIG. 17, when an electrical operation test is conducted, an LCD driver (gate driver with a built-in power supply circuit) if which has a function of driving the gate common terminal of the liquid crystal display panel and a semiconductor test equipment 100 are connected. Under this connection state, the electrical operation test is started. Each of inverter circuits (output circuit) 30 that are the output stages of the LCD driver 1f comprises a level shift circuit 40, a p-channel transistor 50, and an n-channel transistor 51, as shown in FIG. 18, wherein a positive voltage VGH or negative voltage VGL is outputted from a gate output terminal Gx in accordance with an input level H/L.
Gate output terminals G1 to Gn of the LCD driver 1f execute control of display/non-display per line (one pixel line in a horizontal direction as shown in FIG. 16) of the liquid crystal display panel in FIG. 17. Therefore, even if a counter value (setting state) of the LCD driver 1f is changed as shown in FIG. 19, the plurality of gate output terminals G1 to Gn operate so as to exclusively output such a voltage that one terminal among them surely outputs a positive voltage VGH (display voltage) and each of the other terminals outputs a negative voltage VGL (non-display voltage).
In the above-described test for the LCD driver 1f, as shown in FIG. 17, each of the gate output terminals G1 to Gn is connected to a comparator 103 of the semiconductor test equipment 100, and the semiconductor test equipment 100 determines whether a voltage value of each of the gate output terminals G1 to Gn is a positive voltage VGH or negative voltage VGL. Then, if the LCD driver 1f outputs the illustrated voltage values from the respective output terminals G1 to Gn in all counter-value states (setting states) shown in FIG. 19, it is determined that a function of executing the gate outputs in the LCD driver 1f is not abnormal, whereby the test for the gate outputs is completed.
Meanwhile, as high-definition liquid crystal display panels are developed and improved, there is the indication of increasing the number of output pins of the LCD driver. The conventional testing method for the LCD driver is performed by respectively connecting the gate output terminals to the comparators of the semiconductor test equipment, as described above. Further, some of the number of input pins must be allocated the number of channels of the semiconductor test equipment because a voltage from the semiconductor test equipment is applied also to the input pins for operating the LCD driver. Thus, the semiconductor test equipment having more channels in number than the input/output pins of the LCD driver is required and, for example, the semiconductor test equipment having 256 channels cannot test the LCD driver in which the number of gate outputs is 350 pins. Therefore, there is the problem that the above semiconductor test equipment cannot be used for test.
Further, in the LCD driver for driving the liquid crystal display panel which is installed in a small item such as a portable phone, in order to further downsize such a item, a trend is such that all functions (source, gate, and power supply circuit, etc.) for driving the liquid crystal display panel are integrated on one chip, and so the total number of pins of the LCD driver is increased. Therefore, it is necessary to increase the number of channels of the semiconductor test equipment, by newly purchasing an expensive semiconductor test equipment having a large number of channels and by buying options etc. sold through manufacturers. Accordingly, there is the problem that production cost for LCD driver cannot be reduced.
As a solution of the above-described problems, a technique for providing a change-over switch between an element to be tested and a semiconductor test equipment is disclosed in, for example, Patent Document 1 (Japanese Patent Laid-open No. 10-26655). Specifically, it discloses that the test is conducted while the change-over switch sequentially switches each connection between the comparators in the semiconductor test equipment and the output pins of the semiconductor device in accordance with switching signals outputted from a CPU in the semiconductor test equipment. Thereby, even if the output pins of the semiconductor device is more in number than the channels of the semiconductor test equipment, the test can be conducted.